Undiagnosed diseases and rare diseases occur without respect to age, geography, socioeconomic status or level of education. They are frustratingly hard to define scientifically and to classify needs, yet rare diseases affect 30 million people in the USA and the undiagnosed are as yet uncounted. The 2016 census found 42 million people living in the NY/NJ/PA/DE mid-Atlantic region, accounting for 13% of the USA population. We see a need for a UDN Clinical Site based on population and our accounting of >100 children and >100 adults who appear at our institutions yearly with undiagnosed conditions. Referrals to CHOP/UPENN reflect a larger catchment area than just the four-state area and support our pivotal thesis that the regional need is high and we are poised to deliver expertise, coordinated care, and technology to benefit these patients. The modern approach to hospital-based diagnosis, wherein individual clinical teams propose and test organ or system- specific diagnostic concepts, has several limitations. It fails to take advantage of the full clinical abilities of an institution and efficiently use advanced sequencing, bioinformatic strategies, and synergies from collective thinking. The UDN program has brought a collaborative approach to address the needs of the undiagnosed patient population and to mitigate these shortfalls. We propose to utilize technology in a manner that benefits the patient while being respectful of financial constraints and clinician time. This application proposes a Clinical Site operating as part of the UDN that utilizes work flows optimized by the existing UDN with potential efficiencies and strategies for sustainability that may be useful broadly. Aim 1 describes our organization and patient flow that incorporates document management and infrastructure elements. In Aim 2, the evaluation of patients with exome sequencing that has not been informative or who are suspected of a non-Mendelian disorder will be specifically assessed. In Aim 3, strategies for sustainability will be piloted including improved data capture during patient evaluations, a bioinformatic approach to environmental exposures, a ?Human Knockout Screening Core? approach and strategies for the education of future diagnostic physicians. Patients with a recognized disease will have a short stay focused on education and resource identification. Most patients will be stable, but lack diagnosis, and will have a weeklong evaluative inpatient stay typically within our Clinical and Translational Research Center. During the stay, we will perform additional studies and develop a follow-up plan. Acutely ill patients, newborns, and fetuses can be evaluated using stabilization and management in an inpatient critical care unit. Our proposal is directly relevant to the NIH mission since it uses applied knowledge to enhance health, lengthen life and reduce illness and disability in a unique and vulnerable patient population. The proposed Clinical Site has valuable expertise, extensive experience with collaborative networks, strong institutional support and creative solutions to common challenges presented by the undiagnosed patient.